The present invention relates to an exercising device particularly a device for strengthening the muscles associated with the thigh and knee.
Due to the proliferation of contact sports such as football among large masses of the population of this and other countries, a marked increase in the damage being sustained in the knee joint have been evidenced. Physical therapists and trainers have been constantly faced with dealing with damage to the knee joint arising from excessive forces and moments of force in the vicinity of the knee joint.
To strengthen the muscles associated with the knee joint three principle exercises have been used during rehabilitation therapy and knee strengthening.
The most common type of knee strengthening exercise employs the use of a weighted boot, or shoe. The injured person sits in a chair with his injured foor or feet bent so as to be in a normal sitting position. To strengthen and exercise the muscles associated with the knee joint the injured leg would be lifted to its extended position, opposing the downward force of the weighted boot or shoe. This exercise is repeated a number of times, with increasing weight, thereby strengthening the knee joint.
A disadvantage of the use of the weighted boot or shoe involves the undesirable effect of momentum reducing the effective muscular effort required to move the weighted boot or shoe from its bent to its extended position. As the weighted shoe is initially raised from its bent position the muscular activity increases until the momentum of the weighted shoe overcomes the downward force of the weighted shoe so that the shoe actually causes the lower portion of the leg to rise without the requirement of any muscular activity, much as in a pendulum-type movement. Once the weighted boot or shoe begins to swing the "pendulum" nature of the shoe greatly reduces the muscular activity, thereby defeating its initial purpose.
A second method widely used in knee rehabilitation therapy employs the use of a pulley system. An ankle cuff is attached to the injured leg of the user and a cable is connected to the ankle cuff. The cable is passed over a pulley and connected to a weight, typically located behind the user. The user bends his leg and attempts to extend the leg to its straight position, overcoming the restrictive force of the weight.
The disadvantage of the "pulley system" results from the variation of the resistance experienced by the user as the leg travels from its bent position to its extended position. This is the result of the change of the force applied to the ankle as the leg changes its position. When the leg is in its bent position the angle formed between the lower portion of the leg and the cable is approximately 90 degrees. As the leg is raised to its fully extended position the angle between the lower portion of the leg and the cable may be reduced to as little as 20 degrees. The change in angle of this applied force results in the force exerted against the leg when fully extended being only 25% of the resistance applied to the leg when in its fully bent position.
In addition, as in the case of the weighted shoe, the "pendulum" effect further reduces the muscular effort required to oppose the resistive forces of the weights as the leg is moved. With faster movement the deceleration of the leg increases towards the end of its movement, resulting in greatly reduced muscular activity.
Other exercising machines for strengthening the muscles associated with the knee joint also have been available. The disadvantages discussed concerning the exercising devices using the pulley system also occur in the exercising machine, namely the angle between the lower portion of the leg and the restraining force changing as the lower portion of the leg is extended and the "pendulum" effect of the member. Such exercising machines normally comprise a chair-like structure having a lever arm assembly pivotable about a pivot point. The lever arm assembly is located in front of the user's ankles. The user attempts to lift the lever arm assembly by applying pressure to a cushioned projection with the user's ankle. The lever arm assembly is connected to a system of weights for opposing the movement of the lever arm.
A disadvantage of the previously available knee exercising devices was a lack of means for varying the effective resistance experienced by the muscles of the knee as the knee is moved from the bent position to its extended position in the most beneficial manner.
In addition, the previously available exercising devices did not provide for the maximization of the participation of involvement of the muscles associated with the knee joint at various positions of movement of the leg during the bending and lifting activity. As indicated above, the involvement of the muscles associated with the knee during the latter degree of movement of the knee is minimal, due at least in part to the "pendulum" effect discussed previously.
In association with the present invention it has been observed that the involvement of the muscles associated with the knee joint decreases as the lower portion of the leg is initially lifted until such involvement reaches a minimum after about 10 degrees of movement. The involvement of the muscles associated with the knee joint thereafter rises in a sinusoidal manner until a maximum involvement is reached when the angle of movement of the lower portion of the leg approaches approximately 70 degrees. Thereafter the involvement of the muscles once again begins to decrease, again in a substantially sinusoidal manner until the knee is entirely extended. Thus the degree of involvement of the muscles associated with the knee joint follows what may be described as a substantially sinusoidal curve displaced approximately 180 degrees.
In the present invention the force applied to the lower portion of the leg by the exercising machine is varied in such a manner as to provide a substantially uniform effective force to the muscles associated with the knee joint by increasing the applied force in those portions of the movement of the lower portion of the leg where the muscular involvement is less than the optimum, and to reduce the resistance where the involvement of the muscles associated with the knee joint are substantially optimum.
In the preferred embodiment of the invention an off-centered cylindrical member serves as a camming means for varying the effective force applied to the muscles associated with the knee joint. In addition, a guide means associated with a lever arm assembly is employed to maintain the angle at which force is applied to the lower portion of the leg substantially constant.
It is an object of the present invention to provide an exercising apparatus which operates more efficiently than previously available devices.
It is a further object of the present invention to provide a means for varying the effective resistive force experienced by a pivoting lever arm to be moved by the user.
It is another object of the present invention to provide a means for maintaining the angle at which a resistive force is applied to a pivoting member.
Still another object of the present invention is to provide a means for varying the resistive force applied to a pivoting member, such force being capable of being varied so as to optimize the involvement of the muscles associated with the knee joint in opposing the resistive force applied to such a member.
It is yet another object of the present invention to provide an exercising device which is particularly suited for strengthening the muscles associated with the knee joint which is simple to operate.
These and other objects of the present invention will become evident upon the reading of the following description and the accompanying drawings.